Dies for rotary thread roll die machines for producing screws



United States Patent O 3,197,989 DIES FR RTARY THREAD RQLL DIE MA- CHINES FR PRDUCING SCREWS l Frederick William Cooper, Birmingham, England, assigner to @KN Screws and Fasteners Limited, Birmingham,

Engiand, a British company FiledJan. 16, 1963, Ser. No. 251,830 4 Claims. (Ci. 72-104) In my prior application No. 144,123, filed October l0, 196i, there is described and claimed an invention relating to dies for a rotary die thread rolling machine of the generally known type -having a rotary die provided with a thread form around its circumference and co-operating with a stationary die which is ,of segmental form and extends around part of the circumference of the rotary die and wherein a number of blanks are introduced one after another into the space between the rotary die and stationary die so that each blank is rolled through to the exit end of the stationary die and the thread is impressed upon the blank.` l

Such prior application together with the present invention are concerned with the production of screws and the like having a particular form of thread and which screws are described as being spaced thread type. This is a type of screw having a thread form which cannot be produced by thread rolling using a conventional die having a constant cross-section from one end to the other or around its circumference due to the fact that the convolutions of the thread are spaced apart by a substantial distance. Self-tapping screws which have a substantial length of Hat core between adjacent thread convolutions are a good example of this type of screw which I describe as spaced thread type and where the grooves between adjacent threads are not of a sharp character. Screw nails, drive screws, drive nails, and the like also come in this category and are included within the term screws as used herein. n

In this type of screw the corresponding form of the die as previously used has a rib of at top, rounded, or other non-sharp section at the iinishing end to produce the groove between the threads and, as produced on machines having at dies hitherto, it h as been necessary to have a die of changing cross-sectional form from endto-end such that at the starting end of the die the form of the rib is of a sharp V-section to produce the desired initial deforming of the metal with relatively small pressure and this form changes progressively along the length of the die to the nal required at top or other nonsharp form of the ribs at the finishing end of the die.

There lis another method of rolling threads on screws which has certain advantages in economic and rapid production and this involves the use of two or three cooperating rolls each having a thread form around its circumference and the blank being fed into the nip between co-operating rolls. Hitherto it has not been feasible to produce spaced thread type screws by this method of rolling and the object of the invention is to provide improvements which will enable this to be done.

According to the invention there is provided means for producing spaced thread type screws by. rolling between co-operating die rolls wherein one roll has a thread form which is of constant cross-section being somewhat similar to that which is required to produce the spaced grooves and thread of the screw but with the crest of each rib on the die roll being interrupted to give the ribs a degree of sharpness suicient to ensure that the material of the blank is initially deformed with comparatively light pressure.

The invention Iis illustrated in the accompanying drawings wherein:

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FIGURE l is a perspective diagrammatic View of the rolls in a thread rolling machine.

FIGURE 2 shows two fragmentary views of sections on the lines A-A and B-B in FIGURE l.

FIGURE 3 is a perspective diagrammatic view of two rolls in a.` thread rolling machine having a modification of the invention.

FIGURE 4 shows fragmentary -views of sections on the lines AA, B-B in FIGURE 3. Y

The drawings show only the actual thread forming rolls which operate upon -the blanks to produce screws in well-known manner. The machine which incorporates such rolls is of well-known form and is not shown as the construction and operation of such machines is wellknown to those engaged in this art and furtherV reference thereto is unnecessary. l y

The examples shown in FIGURES l and 2 of the accompanying drawings illustrate two driven rolls mounted about spaced parallel axes and there are generally known two types of such machine. In one type, the rolls are of the same diameter and are driven at the same speed and are arranged in the machine so that the axes of rotation of the rolls can be displaced so :as to move the rolls apart and move the rolls back together and in this type of machine with the rolls moved apart` the blank is placed in between the rolls which are then moved together to engage the blank for the rolling of the thread. In the other type of machine, the roll-s rotate about fixed axes and have different diameters or are driven at different speeds orhave a combination of these factors and in this type of machine the blank is fed into .the nip between the rolls and progresses through the nip to the other side thereof as the thread is being rolled thereon. vention is capable of application to both these type of machines employ-ing two cfu-operating die rolls.

In the example of FIGURES l and 2, the one roll 10 has a constant cross-sectional form of die throughout its circumferenceas shown by section A-A in FIGURE 2 and in cross-section this die has V-section grooves 13 corresponding to the actual thread to be produced and such grooves 13 being spaced apart by ribs 14 each of which has its crest interrupted to give it a degree of sharpness which it would not have if the crest were flat. As shown, such interruption may take the form of a further shallow `groove 15 running along the crest of the rib 14 or there may be two or more such shallow grooves. Such grooves 15 are shallow as compared with the depth ofthe V-shaped groove 13 which deiines the actual thread.

`In this form of the invention, the other die roll 11 has a constant cross-sectional die form around its circumference the cross-section (see Section B--B) which corresponds exactly with the desired linished thread form on the'blank and thus it is constituted by V-section grooves 17 spaced `apart by flat top ribs 18.

The degree of sharpness given to the ribs 14 on the one die 10 will be suicient to produce the initial deforming of the metal with relatively small pressure when the blank is iirst contacted by the rolls and as rolling progresses the flat top form of the ribs 18 on the other die 11 will gradually dominate in the'gathering and moving of the metal of the blank to produce the final thread form having at bottom grooves spacingapart the actual thread convolutions.

The above described form of the invention may be used where `the pitch of the screw is not very coarse, that is to say, where the spacing between the grooves of the thread is not very great as compared with the root thickness of the thread convolutions. In this case it is found that the degree of sharpness given to the ribs 14 on the of the metal.

The inl In a case where the screw has a very coarse pitch then it is preferred to use the form of the invention illustrated in FIGURES 3 and 4 wherein the die roll 11 in the machine of FIGURE 1 is replaced with a roll having a special form of die with certain relieved portions. ln this case the die roll is formed in the same way as described in the first example with the crests of the ribs 24 being given the required degree of sharpness by shallow grooves and with the cross-sectional form A-A constant throughout the circumference ofthe roll 20. In this case however, the second die roll 21 would have its circumference made up'from a number of similar segments secured to the roll.

Each such die segment 30 has a cross-sectional form which changes gradually from its starting end, which is the end which rst engages the blank, to its finishing end, which is the end of the segment which last makes engagement with the blank as it leaves the nip between the rolls. At the starting end (see Section A-A) the cross-sectional form is the same as, or similar to, the form of the die on the other roll 20, and it consists of a number of V-shaped grooves 23 spaced apart by ribs 24 each rib having its crest interrupted by one or more relatively shallow grooves 25. Instead of this cross-sectional form being constant throughout the length of each segment 30 however, it changes gradually and the shallow groove or grooves 25 in the crests of the ribs 24 gradually lessen in depth until they disappear completely at about twothirds of the way along the arcuate length of the segmental die (from its starting end) so that over the finishing section (see Section B--B) the cross-sectional form of the die segment provides V-shaped grooves 27 separated by Hat top ribs 28.

With this form of the invention, blanks would be ndexed by known indexing mechanism into the nip 22 between the rolls 20 and 21 so that a blank was correctly positioned at the starting end lof a die segment 30 as this came round in the course of its rotation and in this case the degree of sharpness (from shallow grooves 25) on the ribs 24 of the constant form die roll 20 together with the sharpness provided by the relieved starting section A--A of the segments 30 of the other die roll 21 ensures the initial deforming of the material under relatively light pressure as with the case above described.

In another example the invention may be applied to a 'further type of this machine having three die rolls arranged with axes passing through the apices of a triangle and the blank being rolled in the gap which is defined between the three rolls. In this case two of the rolls may have the constant cross-sectional die form around their circumference such form being as above described for the rolls 10 and 20, and the third roll would have a constant cross-sectional die form corresponding to the desired thread form and having flat top `ribs without any interruption as for roll 11 in FIGURE l. Such machine may be used for producing a spaced type of thread on a relatively long blank which can be fed through the gap between the rolls inthe axial direction to progressively produce the thread along the blank from end-to-end.

What I claim then is: i

1. Means for rolling a threadupon a spaced thread type screw in which adjacent convolutions of the thread rib are spaced apart by a iiatjbottomed groove as herein deined, said-means comprising; a pair of co-operating die-rolls each having a thread form comprising grooves, separated by ribs, extending round its periphery at an 'angle to the axis of the roll corresponding to the helix angle of the thread of the screw, one of said' die rolls having a thread form wherein'each groove has a cross-section corresponding kto the desired cross-section of the thread rib on the screw, and each rib has a cross-section substantially of the form to produce the flat bottomed groove on the screw, but each such rib having its crest interrupted by at least one further groove which extends longitudinally of the rib throughout its length and is of shallow depth as compared with the depth of each groove for producing the thread rib on the screw.

2. Means for rolling a thread upon a spaced thread type screw in which adjacent convolutions of the thread rib are spaced apart by a flat bo-ttomed groove as herein deiined, said means comprising; a pair of `co-operating die-rolls each having a thread form comprising grooves, separated by ribs, extending round its periphery at an angle to the axis of the roll corresponding to the helix angle of the thread of the screw, one of said die rolls having a thread form wherein each groove has a V crosssection corresponding to the desired cross-section of the thread rib on the screw, andeach rib has a cross-section substantially of the form to produce the flat bottomed groove on the screw, but each such rib having its crest interrupted by at least one further groove -of V crosssection which extends longitudinally of the rib throughout its length and is of shallow depth as compared with the depth of each groove for producing the thread rib on the screw; the other of said die rolls having a thread form wherein each groove has a V cross-section corresponding to the desired cross-section of the thread rib on the screw, and each rib has a flat crest to produce the flat bottom groove on the screw.

3. Means for rolling a thread upon a spaced thread type screw in which adjacent convolutions of the thread rib are spaced apart by a fiat bottomed groove as herein defined, said means comprising; a pair of co-operating die-rolls each having a thread form comprising grooves, separated by'ribs, extending round its periphery at an angle to the axis of the roll corresponding to the helix angle of the thread of the screw, one of said die rolls having a thread form wherein each groove has a crosssection corresponding to the desired cross-section of the thread rib'on the screw, and each rib has a crosssection substantially of the form to produce the iiat bottomed groove on the screw, but each such rib having its crest interrupted by at least one further groove which extends longitudinally of the rib throughout its length and is of shallow depth as compared with the depth of each groove for producing the thread rib on the screw, the other of said die rolls having its circumference divided into a number Yof similar die segments, each segment cornprising grooves corresponding to the desired cross-,section of the thread rib on the screw, and ribs, each of which has a cross-section which changes gradually from its starting-end to its iinishing end, the cross-section at the starting end of each rib being substantially -of the form to produce the dat bottomed groove on the screw, but each such rib having its crest interrupted by at least one further groove which is of shallow depth as compared with the depth of each groove for producing the thread rib on the screw, such shallow depth groove decreasing in depth to zero as it extends longitudinally of the rib and the cross-section at the iinshing end of each such rib being of flat crest form to produce the iat bottom groove on the screw. i l 4.` Means for rolling a thread upon a spaced thread type screw in which adjacent convolutions of the thread rib are spaced apart by a iiat bottomed groove as herein defined, said means comprising; a pair of co-operating die-rolls each having a thread form comprising grooves, separated by ribs, extending round its periphery at an angle to the axis of the roll corresponding to the helix angle of the thread of the screw, one of said die rolls having `a thread form wherein each groove has a V cross-section corresponding to the desired cross-section of the thread rib on the screw, and each rib has a crosssection substantially of the form to produce the flat bottomed groove on the screw, but each such rib having its crest interrupted by at least one further groove which extends longitudinally of the rib throughout its length and is of shallow depth as compared with the depth of each groove for producing the thread rib on the screw; the other of said die rolls having its circumference divided 5 into a number of similar die segments, each segment cornpn'sing grooves of V cross-section corresponding to the desired cross-section of the thread rib on the screw, and ribs, each of which has a cross-section which changes gradually from its starting end to its finishing end, the cross-section at the starting end of each rib being sub stantially of the form to produce the at bottomed groove on the screw, but each such rib having its crest interrupted by at least one further groove of V cross-section which is of shallow depth as compared with the depth of each groove for producing the't'hread rib on the screw, such shallow depth groove decreasing in depth to zero as it extends longitudinally of the rib and the cross-section 6 at the finishing end of each such rib being of flat crest form to produce the flat bottom groove on the screw.

References Cited by the Examiner UNITED STATES PATENTS 77,710 5/68 Beecher 80-6 2,182,906 12/39 Unke 80-6 2,422,849 5/43 Plagernann 80-6 2,896,484 7/59 Hanna 80-6 WILLIAM I. STEPHENSON, Primary Examiner.

MICHAEL V. BRINDISI, Examiner. 

1. MEANS FOR ROLLING A THREAD UPON A SPACED THREAD TYPE SCREW IN WHICH ADJACENT CONVOLUTIONS OF THE THREAD RIB ARE SPACED APART BY A FLAT BOTTOMED GROOVE AS HEREIN DEFINED, SAID MEANS COMPRISING; A PAIR OF COOPERATING DIE-ROLLS EACH HAVING A THREAD FORM COMPRISING GROOVES, SEPARATED BY RIBS, EXTENDING ROUND ITS PERIPHERY AT AN ANGLE TO THE AXIS OF THE ROLL CORRESPONDING TO THE HELIX ANGLE OF THE THREAD OF SCREW, ONE OF SAID DIE ROLLS HAVING A THREAD FORM WHEREIN EACH GROOVE HAS A CROSS-SECTION CORRESPONDING TO THE DESIRED CROSS-SECTION OF THE THREAD RIB ON THE SCREW , AND EACH RIB HAS A CROSS-SECTION SUBSTANTIALLY OF THE FORM TO PRODUCE THE FLAT BOTTOMED 